Delay timer



Sept. 27, 1949. H. H. DAVIDS 2,483,126

DELAY TIMER Filed April 10, 1946 Ifiverwtorf: Hugh HDavids, b 77am.197mm His Attovney,

Patented Sept. 27, 1949 I DELAY TIMER Hugh 1!. Davids, Schenectady, N.Y., minor to General Electric Company, a corporation of New YorkApplication April 10, 1946, Serial No. 681,019

4 Claims. (Cl. 175-320) 1 This invention relates to electric circuitsand more particularly to devices for producing electrical effectssimilar to those of inductances and capacitances. This invention furtherrelates to time delay circuits wherein an event is caused to occur at apredetermined time after a first event.

It is an object of the invention to provide apparatus to produce aslowly increasing voltage or current after application of a constantvoltage or current.

Another object of this invention is to provide an electrical circuithaving a very long time delay but which does not require use ofconventional RC or RL circuits having large time constants.

A further object of this invention is to provide a circuit having a verylarge and adjustable time delay when operating in one direction and asimilarly large but independently adjustable time delay when operatingin the reverse direction.

Still another object of this invention is to provide a relay systemwhich connects a utilization circuit to a source of power at apredetermined time after the power is applied and in the event of apower interruption reconnects the utilize.-

tion circuit to the source of power after a time delay determined by theduration of the interruption.

Yet another object 01' this invention is to provide apparatus to producea predetermined long and adjustable time delay in a manner that requiresonly' standard, readily available, low cost, circuit components.

In addition to the above objects, it is the objection of this inventionto provide, by means of simple circuits employing electron dischargedevices, eifective inductances and capacitances of very high valuewithout the actual physical construction of such inductances andcapacitances.

The novel features believed to be characteristic of this invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and method of operation,together with further objects and advantages thereof may best beunderstood by reference to the following description taken in connectionwith the accompanying drawing in which Fig. 1 illustrates an embodimentof the invention adapted for use in a time delay circuit; Fig. 2 is theapproximate equivalent circuit of the embodiment of the invention shownin Fig. 1:" Fig. 3 shows an embodiment of the invention suitable forproducing electrical effects similar to those of a capacitance; and Fig.4 shows a complete time delay control system embodying the principles ofthe invention.

Referring now to Fig. 1 which shows a circuit diagram illustrating anembodiment of this invention, i is an electron discharge device having acathode, anode, and control electrode. The cathode of device I isconnected through resistance 2, source of unidirectional electromotiveforce 3, and switch 4 to the anode thereof, the voltage of source 3being in a direction to make the anode of device I positive with respectto the cathode. Condenser 5, resistance 6, and rectifier l are connectedin series circuit across resistance 2, rectifier I being arranged toconduct when voltage drop across resistance 2 is in the directioncorresponding to conduction in device I. A utilization circuit 8 isconnected across resistance 2 thus to be responsive to the voltage dropthereacross. Resistance 9 is placed across rectifier 'l to provide adischarge path for condenser 5.

The operation of the circuit shown in Fig. 1 can best be understood withreference to Fig. 2 which shows the equivalent circuit of the systemimmediately after switch 5 is closed. In this figure the effect ofdevice l is represented by resistance I0 andvoltage source ii, theserepresenting the internal resistance and voltage respectively of asource producing the same effects on external circuits as device 9.While this representation of device I is not exact, it is Suficientlyaccurate to provide a useful indication of the operation thereof. Thevoltage of source Ii is -ueg where 6g is the negative potential of thecontrol electrode of device i with respect to the cathode. Theresistance of resistance ill is the effective space path resistance ofdevice i, generally designated by the term plate resistance or Tp.

Adding the voltages around the circuit comprising switch 4, device I,resistance 2, and source 3, the following equation is obtained:

E: is the voltage of source 3 in volts, R2 is the resistance of resistor2 in ohms, i1 is the current flow through device I in amperes.

The above equation is written on the assumption that the eflect ofcurrent flow in the shunt path around resistance 2 is negligible ascompared with space path current of device I, a condition that may beobtained by proper choice of circuit components.

The value of 63 can be determined by the current flow through resistance6 inasmuch as it is the 1R drop of this resistance that produces eNeglecting the influence of this current on the voltage drop acrossresistance 2, there results:

i: is the current flow in resistance 6 in amperes, C is the capacitanceof condenser in farads, Re is the resistance of resistor 6 in ohms.

Equation 2 may more conveniently be expressed in operational form (seeGardiner and Barnes, Transients in Linear Systems, Wiley, 1942) whichis:

(3) 11(3) =CR2si(s) C'Rssia(s) for the case of i1 and 2': equal to zeroat the instant of closing switch 4. Solving Equation 3 for the value ofcurrent i2 and computing the IR drop of resistance 6, the value of egbecomes:

CR R 4) as) =Rm s)= f,-;}f

Equation 1, when placed in operational form, hecomes:

(5) E3(S)=7-Lg(8)+(1'p+R2)i1(8) Solving Equations 4 and 5 for thecurrent i(s),

where:

E is the applied voltage,

R is the series resistance in ohms,

L is the series inductance in henries,

i0 is the initial current flow in amperes.

From comparison of Equations 7 and 8 it is evident that the performanceof the circuit of Fig. 2 may be represented by a conventional LR seriescircuit having the following constants:

(9) Equivalent resistance=r,+ R;

Equivalent inductance= CR [r,,+ (1+u) R ch'v'i' 2] Ei rp+ a where To isthe time constant of the circuit acrws resistance 2.

The effectiveness of the circuit of Fig. 1 in simulating the effects oflarge values of inductance can best be explained by v onsideration of anactual circuit component which might be used in Fig. 1. With a value of180 volts at source 3 Equivalent initial current= 4 device I (u=100,Tp=60,000 ohms), the following circuit components might be used:

Rz=10 ohms Ca=2 microfarads Rc=2 X 10 ohms Substituting these values inthe above equations, the equivalent circuit components are:

Roqulv.=1.06 X 10 ohms I Inquiv.=404 X 10 118111188 The time constant(Requm/lcqulv.) then becomes 381 seconds. The initial current obtainedby substituting in Equation 9 is 1.78 10- amperes, a negligible valuecompared to the final current of 170 X 10- am-peres.

While the above values are based on approximations that do not exactlyrepresent the per-- formance of device I throughout its entire operatingcharacteristic, it is evident that the efiects of extremely high valuesof inductance may be simulated by the circuit of Fig. 1. To achieve suchvalue of inductance by usual methods requires inductors of excessivesize inasmuch as the resistance of the inductance must not be so greatas to lower the time constant of the complete circuit. Vieweddifferently, the performance of the above embodiment of this inventioncan be obtained only with an inductance having an inherent time constantof the order of 400 seconds, a value far in excess of the time constantsthat can be economically obtained.

While the circuit of Fig. 1 acts as inductance in so far as voltageincrease across load 8 is concerned, it difiers from a conventional RLcircuit in that no energy s stored in a magnetic field. This constitutesa further advantage of the circuit for the normal high voltage surgesincident to opening an inductive circuit are avoided, therebyeliminating the need for special devices to prevent insulation failureand arcing at switch contacts. In addition, the lack of stored energy inthe circuit permits use of simple control devices to establish the rateat which the system is restored to a quiescent condition after openingswitch 4.

The purpose of rectifier i and resistance 9 in Fig. 1 is to provide adischarge path for condenser 5 in which a controllable time constant isobtained. If switch 4 is opened after condenser 5 is charged or partlycharged, condenser 5 will discharge through resistance 9, device I, andresistance 2. Relatively small current flow will take place throughresistance 5 because the positive control electrode potential at deviceI associated with the charge on condenser 5 causes the controlelectrode-cathode space path resistance of device I to be much smallerthan the ohmic resistance of resistance 6. By proper choice ofresistance 9 the discharge of condenser 5 can be controlled to achieveany degree of time lag desired so that reclosure of switch 4 willrestore urrent flow in resistance 2 having initial value of a desiredrelationship with the period of time during which switch 4 is opened.Since the time constant of discharge depends on the value of resistance9 and the time constant of charge on the value of resistance 5, thesevalues may be independently adjusted to achieve any desired value ofthese constants.

In Fig. 3 a modified form of this invention is shown. This circuitdiffers from that of Fig. 1 only in that condenser 5 and resistance 6are transposed in position. From the standpoint of current flow throughresistance 2 the circuit of and a 6F5 type hi-mu triode electrondischarge Fig. 3 acts as a series RC circuit with a resistance in shuntwith the capacitor. Hence, the voltage transient across load 8 whenswitch 4 is closed resembles that across a resistor in series with acondenser when sudden voltage is applied to the combination.

Other modifications of the circuits of Figs. 1 and 3 will be apparent tothose skilled in the art. If. for example, an inductance is substitutedfor the condenser 5, Fig. 1, the voltage transient across load 8 willcorrespond to that across a resistance when sudden voltage is appliedthrough a condenser. Similarly, the circuit of Fig. 3 will give anefiect similar to an inductance if condenser is replaced by aninductance.

Application of the principles of the invention to a time delay relaycircuit is illustrated in Fig. 4. The purpose of this circuit is toclose relay contacts A and B at a predetermined time after alternatingvoltage is made available at source l2; to instantaneously open thesecontacts upon failure of voltage from source l2; and to reclose contactsA and B at a predetermined time after alternating voltage is reappliedfrom source I2, the reclosure time depending on the lengthof the periodof no voltage. In a practical application of this circuit, contacts Aand B might be in the circuit from source IE to load l3, the lattercomprising rectifier or other circuits leading to the anodes of mercuryvapor type electron discharge devices such as might be used in the pulsegenerator of a remote object detecting system. By use of this control itis possible automatically to apply anode voltage to the rectifiers whenthe cathodes are sufficiently heated while at the same time avoiddestruction of the tubes due to application of voltage when the cathodesare not yet heated. Provision of variable reclosure time depending onthe duration of loss of voltage from source I2 permits automaticoperation of the circuit with minimum loss of operatin time when voltagefrom source |2 fails for an interval of time that does not permit thecathodes of the mercury vapor tubes to cool to room temperature.

Considering in detail the circuit of Fig. 4, voltage from source I2 isapplied to potentiometer l3 and to terminals l4 and I5. This voltagecauses rectifiers l8 and IE to charge condensers l6 and I! respectively.The charge on condenser i1 causes the anode of electron discharge device20 to become positive with respect to point |5 whereas the charge oncondenser l6, acting through resistance 2|, causes the cathode of device20 to become negative with respect to point- |5. Hence, the circuitcomprising potentiometer l3, rectifiers I8 and HI, and condensers l6 andI1 causes the anode of device 20 to-become positive with respect to thecathode by an amount determined by the potential of source 2. Thecircuit comprising resistances 2 I, 24 and 32, rectifler 23, andcapacitor 22 will be recognized as identical with that Of Fig. 1. Hence.current flow through resistance 2| and device 20 will slowly increaseafter potential from source I2 is applied.

The control electrode of gaseous discharge device 26 is connected to thecathode of device 20 whereas the cathode of device 26 i connected topoint l5. Hence, with device 20 in a non-conducting condition, thecontrol electrode of device 26 is negative with respect to the cathodeby an amount depending on the charge of condenser l6. However, ascurrent flows through device 20, and hence through resistance 2|, avoltage drop appears across that resistanc which tends to make thecathode of device 20 less negative with respect to point II. The rate ofthis current and 7 1y from A.-C. source l2 through resistance 28.

When current flow takes place through device 26, relay coil 21 isactuated, thereby causing contacts A and B to close and apply voltage toload l3. In addition contacts C are closed and the control electrode ofdevice 26 caused to be of equal potential with the cathode. This causesthe control electrode of device 26 to lose control and conductioncontinues therethrough independently of the voltage drop acrossresistance 2|. It will be understood, of course, that contacts C are notessential to operation of the system but are considered desirable toavoid relay chatter.

It is the purpose of condenser 29 across relay coil 21 to smooth thecurrent flow through that coil and thereby to reduce chatterin of therelay armature. Condensers 30 and 3| prevent voltage surges which mayappear when voltage from source I2 is reapplied to the circuit frominstantaneously tripping device 26. Resistances 33 and 34 provideleakage paths for discharge of condensers H and I6 respectively.

As described above with relation to Fig. 1, the time constant of voltagebuild-up across resistance 2|, Fig. 4, depends on the time constant ofthe circuit comprising resistance 24 and capacitor 22. Hence, byadjustment of the value of resistance 24, the time interval betweenapplication of voltage from source I2 and the operation of relay 21 canbe adjusted at will.

If voltage from source l2 fails, operating voltage is no longeravailable across device 26 and relay 2'! drops out, therebydisconnecting load I3 and opening contacts C. In addition, condenser 22commences to discharge through resistance 32 and the controlelectrode-cathode space path of device20. If the voltage from source I2.is off for a long period of time before it is reapplied, the charge oncondenser 22 is completely lost and full time delay between thesubsequent application of voltage and operation of device, 26 isobtained. On the other hand, if the voltage from source I2 is reappliedbefore condenser-22 dis charges, the time required to build up voltagethereacross is reduced and device 26 operates aftera shorter interval oftime. Hence the time required to apply voltage to load |3 varies inaccordance with the time during which voltage is lost across source |2.

If load I3 consists of the anode potential source to be applied tomercury vapor rectifier tubes, the time constant of discharge ofcondenser 22 through resistances 32 and 2| and the controlelectrode-cathode space path of device 20 is chosen with respect to thecooling characteristics of the mercury vapor tube heaters, thus causingrelay 2! to operate just as soon as the anode voltage may be safelyapplied. The value of this time delay may be chosen without influencingthe time delay between application of voltage from source l2 andoperation of relay. 2! by varying the value of resistance 32. I

From the above discussion it is evident that the circuit of Fig. '4provides the following time-delay action:

amass source I 2, voltage is applied to load I! after a predeterminedtime interval which may be adjusted by varying the value of resistance24.

2. On loss of voltage from source l2, load I3 is immediatelydisconnected from source I2.

3. On reapplication of voltage from source l2, voltage is applied toload l3 after a time delay depending on the time period during which novoltage is applied from source l2, the value of this delay beingindependently adjustable by varying the value of resistance 32.

While I have shown and described certain particular embodiments of myinvention, it will of course be understood that I do not wish to belimited thereto since various modifications both in the circuitarrangement and the instrumentalities employed may be made and Icontemplate by the appended claims to cover any such modifications asfall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A time delay circuit comprising an electron discharge device havingan anode, a cathode, and a control electrode, means for selectivelyapplying a positive potential to said anode relative to a fixedreference point, a first impedance connecting said cathode to saidreference point, a timing circuit connected across said first impedance,said timing circuit serially comprising a second impedance, saidrectifier being poled to conduct in the direction towards said referencepoint, a discharge impedance connected across said rectifier, saidcontrol electrode being connected to a point on said timing circuitwhich is rendered negative with respect to said cathode in response toflow of charging current in said capacitor, the time constant of saidtiming circuit being such that application of said potential to saidanode causes an increasing current to flow in said device until saidcapacitor charged to a predetermined maximum potential, a load deviceenergized in response to rise in current in said first impedance above apredetermined minimum value, and means including said dischargeimpedance and the grid-to-cathode path of said device for dischargingsaid capacitor at a predetermined rate unon interruption of saidpotential.

2. A time delay circuit comprising an electron discharge device havingan anode, a cathode, and a control electrode, means for selectivelyapplying a positive potential to said anode relative to a fixedreference point, a first resistance connected from said cathode to saidreference point, a timing circuit also connected from said cathode tosaid reference point and serially comprising, in the order named, asecond resistance, a rectifier, and a capacitor, said rectifier beingpoled to conduct in the direction towards said reference point,

a third resistor connected in shunt across said rectifier, said controlelectrode being connected to the common junction point of said secondand third resistors and said rectifier, the time constant of said secondresistor and said capacitor being such that application of saidpotential to said anode causes an increasing current to fiow in saiddevice until the charge 'on said capacitor rises to a predeterminedmaximum value, a load device energized in response to rise in current.in said first resistance above a predetermined minimum value, and meansincluding said third resistor and the grid-to-cathode path of saiddevice for dischargin said capacitor at a predetermined rate uponinterruption of said potential.

3-. A time delay circuit comprising an electron discharge device havingan anode, a cathode, and a control electrode, means for selectivelyapplying a positive potential to said anode relative to s fixedreference point, a first resistance connecting from said cathode to saidreference point, a timing circuit also connected from said cathode tosaid reference point and serially comprising, in the order named, acapacitor, a rectifier, and a second resistance, said rectifier beingpoled to conduct in a direction towards said reference point, a thirdresistor connected in shunt across said rectifier, said controlelectrode being connected to the common Junction point of saidcapacitor, said third resistor and said rectifier, the time constant ofsaid second resistor and said capacitor being such that upon applicationof said potential to said anode causes an increasing current to flow insaid device until the charge on said capacitor rises to a predeterminedmaximum value, a load device energized in response to rise in current insaid first resistance above a predetermined minimum value, and meansincluding said third resistor and the grid-to-cathode path of saiddevice for discharging said capacitor at a predetermined rate upon theinterruption of said potential.-

4. A time delay circuit comprising an electron discharge device havingan anode, a cathode, and a control electrode, means for selectivelyapplyins a positive potential to said anode relative to a fixedreference point, a first resistance connected from said cathode to saidreference point, a timing circuit also connected from said cathode tosaid reference point and serially comprising, in the order named, asecond resistance, a rectifier, and a capacitor, said rectifier beingpoled to conduct in the direction towards said reference point, a thirdresistor connected in shunt across said rectifier, said controlelectrode being connected to the common junction point of said secondand third resistors and said rectifier, the time constant of said secondresistor and said capacitor being such that application of saidpotential to said anode causes an increasing current to flow in saiddevice until the charge on said capacitor rises to a predeterminedmaximum value, a normally-open load control relay having an operatingcoil energized in response to the current in said first resistance, saidrelay being operated to close load-controlling contacts when the currentin said first resistance rises above a predetermined minimum value, andmeans including said discharge impedance and the grld-to-cathode path ofsaid device for discharging said capacitor at a predetermined rate uponinterruption of said potential.

HUGH H. DAVIDS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PA'I'ENTS Number Name Date 1,939,462 Ramsay Dec. 12, 19332,114,883 Knowles Apr. 19, 1938 2,279,007 Mortley Apr. '1, 1942 FOREIGNPATENTS Number Country Date 408,624 Great Britain Apr. 9, 1934

